This invention relates to a process for the repair of breakages or cracks in silicon carbide brick structures and mortars therefor.
In smelting, particularly zinc smelting, silicon carbide bricks are used for furnace structures in the vertical distillation process and electrothermal process and attached equipments thereof. Further, in the installation of multistage rectification towers where zinc produced by the above processes is further rectified, silicon carbide bricks of good heat conduction, mechanical strength and antispalling are used.
Particularly, retorts in the vertical distillation process, condensers in the electrothermal process and the tray and condenser in the rectification tower constitute major apparatus portion, which are very important for each of the processes and therefore, using silicon carbide bricks is an indispensable requirement. Silicon carbide mortars are used in joints between bricks.
The silicon carbide brick is oxidized on its surface at an elevated temperature under an oxidizing at atmosphere, and the extreme case is that the oxidation reaction advances towards the inside and therefore the brick is brought to swelling and breaking. Even when the oxidation is confined to the surface of the bricks, the oxidation layer has a heat conductivity reduced to about one tenth so that heat efficiency is reduced. Therefore the brick surface is usually covered with a clay type glaze.
The retort, condenser, tray and the like are heated to a high temperature of 600.degree.-1,300.degree. C. and exposed to vaporous metal, e.g. zinc vapor. The largest disadvantages of the silicon carbide brick are sensitivity to thermal change at high temperatures and to local heating so that a crack and a break in joints take place at a temperature change of about 30.degree. C./hr. Further, since the interior of these brick structures is under a pressure of 10 to hundreds mm H.sub.2 0 higher than the outside due to zinc vapor, cracking and breaking in joints result in leaking of zinc vapor or molten zinc escape. Accordingly, it is necessary to discontinue the operation of the installation or build a new furnace.
For preventing the leakage of vaporous metal or molten metal through cracks or breaks in joints, there has been heretofore employed a method of sealing breakages to be repaired by hot spraying or coating an alumina or silicon carbide type mortar. However, with these mortars a satisfactory sealing effect on the leakage of vaporous metal or molten metal cannot be obtained.
Further, in some cases the repair working itself brings about a drastic thermal distortion to cause new cracks. Also, when a large amount of mortar is applied by spraying, the surface of silicon carbide brick is covered with a coating of low heat conductivity and as a result, in addition to lowering of efficiency of the installation, normal combustion in the furnace is hindered because of accumulating of the mortar.